hibernate.hbm2ddl.auto=update不能自动生成表结构

在写上篇文章《spring整合springmvc和hibernate》的时候，曾遇到一个问题

INFO: Server startup in 8102 ms
Hibernate: insert into t_user (name, password) values (?, ?)
Mar 31, 2018 5:47:19 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [springmvc] in context with path [/mvn-ssh] threw exception [Request processing failed; nested exception is org.hibernate.exception.SQLGrammarException: could not insert: [com.mvn.entity.User]] with root cause
java.sql.SQLSyntaxErrorException: Table 'mvn.t_user' doesn't exist
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:536)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:513)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:115)
    at com.mysql.cj.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:1983)
    at com.mysql.cj.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1826)
    at com.mysql.cj.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2034)
    at com.mysql.cj.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:1970)
    at com.mysql.cj.jdbc.PreparedStatement.executeLargeUpdate(PreparedStatement.java:5001)
    at com.mysql.cj.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1955)
    at org.apache.commons.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:97)
    at org.apache.commons.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:97)
    at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:93)
    at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:56)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2346)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2853)
    at org.hibernate.action.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:71)
    at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:273)
    at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:320)
    at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:203)
    at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:129)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
    at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
    at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
    at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:713)
    at org.hibernate.impl.SessionImpl.save(SessionImpl.java:701)
    at org.hibernate.impl.SessionImpl.save(SessionImpl.java:697)
    at com.mvn.dao.UserDao.save(UserDao.java:19)
    at com.mvn.service.UserService.save(UserService.java:18)
    at com.mvn.service.UserService$$FastClassByCGLIB$$7706a99b.invoke(<generated>)
    at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:688)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:621)
    at com.mvn.service.UserService$$EnhancerByCGLIB$$8b9eb23e.save(<generated>)
    at com.mvn.controller.SaveUser.saveUser(SaveUser.java:23)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:442)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1083)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:640)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

说是表t_user不存在，也就是说hibernate并没有自动生成表结构，hibernate.hbm2ddl.auto=update不起作用，但是把update改为create就能自动生成。

通过在网上查询，有人说是方言错误，需要将

hibernate.dialect=org.hibernate.dialect.MySQLInnoDBDialect

改为

hibernate.dialect=org.hibernate.dialect.MySQL5Dialect

但是我本来就是这样写的，肯定是其他原因也会导致hibernate.hbm2ddl.auto=update不起作用。

终于在几乎千篇一律的文章中找到了一篇不一样的，原因是数据库中已经有相同名字的表了（可能这张表是属于别的用户）

于是我到别的里面查，果然在另外一个里面确实存在t_user表了，

解决方案：

将既存t_user改为t_user1或者将这次的表名字修改下，

然后再执行这次代码，成功！！